Larson-Skold Corrosivity

Other indices proposed that have tried to overcome the basic limitations of LSI include the Stiff and Davies Saturation Index, Larson and Buswell Index, Puckorius (Practical) Scale Index, Oddo-Tomson Index, and Larson-Skold Corrosivity Index, some of which are discussed briefly here. 

Larson-Skold index. The Larson-Skold index describes the corrosivity of water toward mild steel. The index is based upon evaluation of in situ corrosion of mild steel lines transporting Great Lakes waters. The index is the ratio of equivalents per million (epm) of sulfate (S04 ) and chloride (Cl ) to the epm of alkalinity in the form bicarbonate plus carbonate (HC03 + 003 ). 

As outlined in the original paper, the Larson-Skold index correlated closely to observed corrosion rates and to the type of attack in the Great Lakes water study. It should be noted that the waters studied in the development of the relationship were not deficient in alkalinity or buffering capacity and were capable of forming an inhibitory calcium carbonate film, if no interference was present. Extrapolation to other waters, such as those of low alkalinity or extreme alkalinity, goes beyond the range of the original data. 

Skold and Larson" in studies of the corrosion of steel and cast iron in natural water found that a linear relationship existed between potential and the applied anodic and cathodic current densities, providing the values of the latter were low. However, the recognition of the importance of these observations is due to Stern and his co-workerswho used the term linear polarisation to describe the linearity of the rj — i curve in the region of E o , the corrosion potential. The slope of this linear curve, AE — AJ or Af - A/, is termed the polarisation resistance, / p, since it has dimensions of ohms, and this term is synonymous with linear polarisation in... 

Larson, T. and Skold, R., Laboratory Studies Relating Mineral Quality of Water to Corrosion of Steel and Cast Iron," Corrosion, June 1958, p. 43. 

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